(a) Field of the Invention
The present invention relates to an electron emission device. More specifically, the present invention relates to a display device using a field emitter array.
(b) Description of the Related Art
Generally, there are two kinds of electron emission device (EED). One uses a thermionic cathode as an electron source and the other uses a cold cathode as an electron source. Also, in the EED using a cold cathode, there are the field emitter array (FEA) type, the surface conduction emitter (SCE) type, metal-insulator-metal (MIM) or metal-insulator-semiconductor (MIS) type, and ballistic electron surface emitting (BSE) type.
In particular, the EED is being considered as a next-generation display because it uses light emission of fluorescent bodies by electron beams as does the cathode ray tube (CRT) to have the excellent characteristics of the CRT and to realize a flat panel display of low power consumption without any image distortion. It also has some satisfactory characteristics with regard to large viewing angle, fast response time, high brightness, high contrast, and small panel thickness.
The typical EED is composed of a triode structure having cathode, anode, and gate electrodes. More specifically, the cathode electrode that is generally used as a data electrode is formed on a substrate. An insulation layer having a contact hole and the gate electrode generally used as a scan electrode are integrated on the insulation layer. Additionally, an emitter used as an electron source is formed inside the contact hole and is connected to the cathode electrode. Alternatively, the gate electrode can be a data electrode and the cathode electrode can be a scan electrode. That is, a cathode electrode can be one of a scan electrode and a data electrode, and a gate electrode can be the other according to structure of the EED.
The EED of this structure concentrates a high electric field on the sharp-tip cathode, that is, the emitter, to emit electrons by the quantum-mechanical tunneling effect, which electrons are accelerated by a cathode-anode voltage and collide with red (R), green (G), and blue (B) fluorescent films formed on both electrodes to emit light from the fluorescent body and to display an image.
The brightness of the image formed from light emission of fluorescent bodies as caused by collision of the emitted electrons with the fluorescent film changes according to the value of an input digital video signal. More specifically, the value of the digital video signal is composed of 8-bit RGB data, i.e., 0(00000000(2)) to 255(11111111(2)), which 256 digital values realize 256-gray-scale representation and color brightness.
Pulse width modulation (PWM) or pulse amplitude modulation (PAM) is generally used to control the brightness represented by the value of the digital video signal.
PWM is a technique to modulate the pulse width of driving pulses applied to display input image data according to counted clock signals output from a driving IC, to achieve gray scale representation. In PWM, the number of counted clock signals is equal to the total number of gray scale levels, and in most cases, 8-bit signals are input to realize a 256-gray-scale full color image.
The time required for generating the total number of counted clock signals is the on-time applied to the display panel through a data electrode. For counted clock signals of an even-spacing cycle, driving pulses of the same pulse width for all data of 0 to 255-gray levels are applied. For counted clock signals of a non-even-spacing cycle, for example when the spacing width is increased in the low gray scale level and decreased in the high gray scale level, the pulse width of the driving pulse by gray scale levels increases in a part of the input image data of a low gray scale level but decreases in a part of the input image data of a high gray scale level. Hence, the low gray scale of the data is better represented on the actual display panel to enhance the ability of brightness representation according to the gray scale on the dark image.
In this conventional PWM method, the cycle of counted clock signals is constant irrespective of input image data because no information is provided about the counted clock signals of which cycle must be raised among the gray scale levels of 0 to 255. This makes it impossible to effectively control brightness according to the input image data.